1. Field of the Invention
The present invention relates to a rotor hub to which a disk is attached, a motor having the rotor hub, and a disk driving device having the motor.
2. Description of the Related Art
Conventionally, a disk driving device such as a hard disk drive includes a spindle motor (hereinafter, referred to as a “motor”) for driving a storage medium disk attached to a rotor hub. The rotor hub is usually made of a metal material such as aluminum or aluminum alloy. The disk is affixed to the rotor hub via a clamper or the like while the bottom surface of the disk is in contact with the rotor hub.
In the motor such as one described above, a field magnet and a yoke which prevents a loss of a magnetomotive force by covering outer and inner sides of the field magnet are arranged below a disk loading portion. The field magnet generates a torque between an armature and the field magnet. The yoke is made of a ferromagnetic material (e.g., stainless steel) and is affixed to the rotor hub by crimping or press fitting.
In the motor such as one described above, if the yoke is deformed relative to the rotor hub due to a difference in a coefficient of thermal expansion of the yoke and that of the rotor hub, a force generated due to the deformation of the yoke may be conducted to the disk loading portion, thereby deforming the disk loading portion. Also, the disk loading portion may be deformed due to a load applied when affixing the yoke thereto. When the disk loading portion is deformed, the disk may be rotated with a runout which can cause an error in reading and/or in writing of information on the disk.
In order to prevent such deformation, a technique has been conventionally available in which a space is provided between an upper end of a yoke and a hub having a projecting portion so as to maintain the space therebetween, whereby no force will be conducted from the yoke to the hub preventing the deformation of the disk loading portion. Also, a technique has been conventionally available in which a collar portion of a hub is securely sandwiched by a yoke and a driving magnet in order to affix the yoke without applying a large load on the hub.
Further, a technique has been conventionally available in which, in a magnetic disk driving device, a rotor yoke is crimped to a hub, and a portion of a top end of the rotor yoke is in contact with the hub. Also, a technique has been conventionally available in which, in a magnetic disk driving device, a back yoke which protrudes farther outward than a circumference of a hub is affixed to the hub. Also, a technique has been conventionally available in which a layer of adhesive is provided at a portion in which a hub and a yoke are joined to one another to prevent a vibration generated in a magnet while the magnet is in motion from being conducted to the hub.
Despite these conventional techniques, however, although a heat deformation of the disk loading portion can be minimized to a certain extent, it is very difficult to further minimize the deformation of the disk loading portion because a connecting portion between the yoke and the hub is near the disk loading portion and, therefore, a force generated by the yoke is easily conducted to the disk loading portion.
The deformation of the disk loading portion occurring when the yoke is connected to the hub in a conventional disk driving device can be minimized. However, the heat deformation occurring after the connection is made cannot be minimized.